High resolution image source

ABSTRACT

Image source, for converting image data in the form of serial charges into a high-resolution imagewise light pattern, combines semiconductor charge-coupled devices for receiving the charges, associated small-scale field emission arrays for converting the charges to imagewise pattern of electron emissions, an electron multiplier for intensifying the electron emissions, and a luminescent phosphor layer susceptible to light output according to the impact of the intensified electron emission. The light output may be directed onto a photosensitive image recording medium to provide for image recording. Second and third embodiments of the contemplated image source provide light output that forms an image to be viewed directly.

This is a Continuation of application Ser. No. 07/696,428, filed May 6,1991 now U.S. Pat. No. 5,818,500.

FIELD OF THE INVENTION

The present invention relates generally to image sources and morespecifically relates to apparatus for converting an electrical signal,representing an image, into a pattern of light corresponding to thatimage.

BACKGROUND OF THE INVENTION

Devices have been proposed to convert an electrical signal,representative of image information, to a corresponding imagewisepattern of light. Such conversion devices, hereinafter "image sources",can provide a light image or portion thereof for image display,imagewise exposure of a photosensitive medium, or for delivery to animage information transmission or sensing system.

For example, in a typical image recording system, an image source may beused to provide a pattern of light that exposes and thus alters aphotosensitive recording medium in an imagewise fashion. The desiredimage may be composed and made visible on the recording medium, such asphotographic film, or upon other types of receiving media from which theimage is transferred to a hard copy medium, such as those used in theelectrophotographic art.

If used as an image display device, an image source is expected toproduce a light pattern that is directly viewable by a human observer.The pattern may be composed by accumulating line-by-line portions of theimage to be displayed, or an entire image frame may be producedsubstantially at once. For example, planar image display devices havefound application as alpha-numeric displays.

Electro-optical Element Arrays

Some conventional image sources are constructed from arrays of minuteelectro-optical elements, such as liquid crystal light shutters, each ofwhich have a limited output area of predetermined geometry andarrangement that selectively transmit or attenuate light from a diffuselight source. Most other image sources have been constructed from arraysof electro-optical point-source elements such as light-emitting diodesthat directly generate light.

The foregoing arrays are typically arranged linearly, known as a striparray, or in rows and columns, to form an area array. Each image sourcearray element is addressable according to its position in a row (in astrip array) or a row and column matrix (in an area array). Each elementis activated by an addressing scheme for activating at least one addressline for each point in the array. Electro-optical elements that employactive binary elements also must be individually switched between "ON"to "OFF" states in accordance with appropriate electrical input signalsthat are applied directly to the individual elements.

In a linear array, there is therefore at least one signal electrode foreach element. In an area array, at a minimum there are "X-Y" addressingsignals used to power electrode strips that control the transmission ofrespective row and column signals to correspondingly-addressed elements.By application of suitable potentials to two or more sets of electrodes,individual elements of the display can be switched on or off in aline-by-line manner to produce a complete image.

Such addressing requirements limit the geometry and density of sucharrays, and the type and amount of image information that they canproduce. The conventional image source therefore must utilize extremelylarge numbers of signal electrodes, and complex addressing and controlmethods and circuitry, if they are to meet the stringent requirements inmodern, high-density, high resolution imaging applications.

Another disadvantage of conventional image sources is that theaforementioned arrays, whether they be of the linear or area array type,are difficult and costly to manufacture if they are to include asufficient density of light source elements for the production of a highresolution image. In practice, their light output is typically limitedin resolution to approximately 400-600 dots per inch (DPI).

A third disadvantage is the difficulty in achieving accurate, high-speedactivation and control of the many individual elements that are selectedto comprise an image pattern. This is especially difficult forprocessing image information that is dynamic, such as that found invideo imaging systems. For example, in an area array, a row and columnaddressing system can be consistent with the addressing techniques usedin solid state random access memories and requires little supportcircuitry to operate one emission or transmission point at a time.However, there is an inherent disadvantage in that such an addressingscheme becomes quite limited when the image pattern to be producedbecomes more complex, more detailed, or more transitory.

For example, light emitting diodes (LED's), each of such minute size andarranged in an array of sufficient density so as to provide a highresolution image, are costly to produce as a linear array and areprohibitively expensive if organized as an area array. Theinterconnection and addressing requirements for an area LED array, notto mention the support circuitry, is also expected to be extremelycomplex and expensive.

Another inherent disadvantage is that each point in a conventional imagesource array may be called upon to activate for only a brief moment. Theinstantaneous brightness of any element must be achieved quickly and toa very high level--a requirement that has not been met in the presentstate of the art.

Further, conventional image sources are constructed from elements thathave relatively large dimensions; these discrete elements are inherentlynot amenable to high packing densities, and are more prone tomanufacturing defects or failure when such densities increase. Only oneelement is typically dedicated to producing one picture element("pixel") of the image. Hence, upon the failure of any one image sourceelement, such as an LED, a full "pixel" of image information ispermanently lost. The overall image quality of the array is quicklydegraded as more and more elements fail.

Conventional image sources that use active electro-optical elements arealso relatively inefficient in converting an impressed signal to light,and therefore require large surges of driving current for theiractivation. Such drive currents require the use of specially-designedpower supplies. A large proportion of the current in such power surgesis dissipated as heat, which is undesireable and must be removed by theuse of heat sinks.

Additionally, the driving signal to conventional active devices such asLED's is typically modulated to circumvent their inherent nonlinearityin light output. The typical electro-optical element is operatedaccording to, for example, pulse-mode modulation. Activation signals forbinary elements are abrupt and require a very fast, complex switchingmatrix or a multiplexing apparatus. The activation signal, pulsed by acurrent source circuit at a very high rate usually creates significantlyundesireable electromagnetic interference (EMI).

Still another disadvantage of an image source based on electro-opticalelements is that the array cannot generate true primary colors. LED'sthat emit in the blue region of the spectrum have only recently beendeveloped and are not practically suited for most applications.

Cathodoluminescent Image Sources

Cathodoluminescent devices are also known for use as image sources inimage display and image recording applications. For example, in U.S.Pat. No. 4,803,565, a conventional electrostatic recording apparatus isdisclosed as having an optical write head having light emission elementsdisposed in rows, for forming an electrostatic latent image on aphotosensitive material. The construction of the write head is said toinclude anode patterns formed within an evacuated, closed case. Theanode patterns are coated with fluorescing material. A thermioniccathode is heated by an electric current flowing therein, causing theemission of thermal electrons. When the cathode is grounded and apositive voltage is impressed on the anode electrodes, the thermalelectrons collide with the florescing material, causing it to fluoresce.To achieve a selected pattern of florescence, the anode electrodes mustbe distributed in spaced, parallel insulated intervals in an alternatingrelationship. A circuit must be provided for selectively impressing apredetermined positive voltage individually to each anode electrode toprovide a predetermined pattern of light emission corresponding to thedesired image dot pattern in an electrostatic latent image on thephotosensitive material.

Hence, activation signals for each anode electrode element must beconducted in a complex switching matrix and may require multiplexing.Such apparatus is costly, difficult to manufacture and operate, andgenerates undesireable electromagnetic interference (EMI). Thermionic("hot") cathode designs are also very inefficient, and suffer fromstructural degradation, device failure modes, and many other effects ofthe heat dissipated at the cathodes.

Much larger scale cathodoluminescent image displays, such as the cathoderay tube (CRT), are known to include a cathodoluminescent layer at theface of the screen which is written by a movable electron beam emittedfrom a thermionic cathode gun. Unlike the aforementioned arrays ofelectro-optical elements, a CRT will rather easily display imageinformation in the form of a rapidly time-varying electrical signal in arasterized format. That is, individual electrodes for each pictureelement are not used and matrixing is unnecessary. Instead, thecontrolled deflection of the electron beam allows the CRT to convertsignals representative of a rapidly changing image to a displayed imagehaving at fairly high light intensity. The cathode ray tube (CRT) hasfound widespread application mainly as a low-resolution image displaysystem.

However, large scale cathodoluminescent image sources suffer from manyintractable disadvantages. No large-scale cathodoluminescent device hasbeen successfully designed or fabricated as a source of veryhigh-resolution light images. Their thermionic electron source designsubstantially limits the efficiency of the device as well as itsoperating life. A CRT, for example, requires a high voltage source onthe order of 10,000 to 30,000 volts. Also, these devices require alarge, bulky glass envelope so as to contain the electron beam in a highvacuum environment.

There has been significant interest and much effort expended indeveloping satisfactory "flat panel displays" which obviate the depthrequirement of a typical large-scale cathodoluminescent device, whilehaving comparable or better light emission characteristics, e.g.,brightness (efficiency), resolution, power requirements, etc. Some flatpanel image sources have been produced which utilize single, multiple orribbon beams directed initially essentially parallel to the plane of thedisplay and then caused to change directions essentially in the Zdirection to address appropriate areas of the display target eitherdirectly or by way of a selecting and/or focusing grid structure.Examples are the Aiken and Gabor devices, U.S. Pat. Nos. 2,928,014 and2,795,729, respectively, using single guns, and the RCA multibeamchannel guide system as exemplified by U.S. Pat. Nos. 4,103,204 and4,103,205.

The major drawbacks of flat panel CRT systems still reside in theirconstruction and/or their complex electrical and electron/opticalcontrol requirements, their dependency on a thermionic cathodestructure, and the requisite ancillary apparatus for providing the highvoltage fields necessary to precise electron beam steering. Known flatpanel displays are useful for some minor display applications but havenot been produced in panels that offer image resolution and imagequality in excess of a conventional CRT. Designers of image display andrecording apparatus therefore have been limited to the above-describedarrays of electro-optical devices as previously described.

Field Emitter Arrays (FEA)

In search of a replacement for the conventional thermioniccathodoluminescent image source, researchers in the field of vacuummicroelectronics have pursued the development of microfabricated coldelectron sources capable of providing vacuum current densities that areorders of magnitude above those provided by thermionic electron sources.Vacuum microelectronics combines the arts of semiconductor solid-stateprocessing and fabrication techniques with vacuum ballistic electrontransport. Arrays of micron-scale, high-current-density cold emittershave been proposed to obviate inefficient and cumbersomelow-current-density thermionic cathode designs.

Recent progress in the microfabrication of a low-voltageintegrally-gated vacuum electron emitter has resulted in increasinginterest in what is known as field emission cathodes (FEC), a pluralityof which are constructed and arranged as a field emitter array (FEA).Conventional FEA's are arrays of tightly-packed, gated vacuum fieldemission devices wherein the field emission is based on the quantummechanical tunneling of electrons through the emitter/vacuum interfaceupon the application of a high electric field. With field strengths of5×10⁷ V/cm, extremely high current densities can be extracted: up to 10⁶A/cm² in metals. One advantage of field emission is that little energyis expended in extracting the electrons through the surface.

The simplest field emitter array consists of a plurality of extremelysharp micron-scale vacuum electron field emitter tips, each having anintegrated conducting extraction gate on an associated dielectric layer.The electron emission is controlled by varying the gate-to-emittervoltage. Electrons emitted from the tip travel ballistically in thevacuum to a drain.

Small-scale cathodoluminescent image display devices have been proposedthat comprise baseplates covered with field emitter arrays, each ofwhich is studded with many conic, submicron-sized emitters. When thespace between the backplate and a phosphor-coated faceplate isevacuated, and an appropriate voltage is established between the plates,ballistic electrons emitted from the cathodes travel in a relativelystraight line to activate the phosphor dots that comprise the pixels onthe faceplate. Each pixel thus has a dedicated array of cathodes.

However, other problems have prevented such a structure from being apractical image source. The cathode emitter tips are nonuniform in theiroutput and typically are difficult to manufacture in inexpensive arraysfor uniform image generation over a large areas. Furthermore, there isthe long-standing problem, common to the aforementioned electro-opticalelement arrays, in assigning and/or switching discrete portions of anapplied electrical signal to the many respective points in the fieldemitter array. The requisite multiplexing and/or addressing schemes, asdescribed hereinabove, are undesireably complex and expensive when usedto selectively activate the field emitter arrays. Moreover, suchmatrixing schemes can require the switching or modulation of fairly highvoltage potentials. The task of switching such potentials at a high rateis quite difficult in practice.

Further background on field emission structures may be found in U.S.Pat. Nos. 3,789,471; 3,812,559; 3,453,478; and 4,857,799; and in VacuumMicroelectronics 1989: Second International Conference on VacuumMicroelectronics, Turner (ed.), 1989.

Solid State Displays

In a different approach, disclosed in U.S. Pat. No. 3,792,465 andentitled Charge Transfer Solid State Display, a solid state displayincorporates a semiconductor charge shift register. Information fordisplay is read into the semiconductor charge devices by shift registeraction in the form of minority carriers. In one embodiment, thesubstrate comprises a unitary body of semiconductor material havinglight-emitting characteristics. Means are provided for reverse biasingthe p-n junction to near avalanche breakdown such that the minoritycarriers corresponding to the data to be displayed trigger avalanche andprovide a large quantity of minority carriers for producing a visibledisplay upon recombination with majority carriers.

Nonetheless, there is a major problem associated with a semiconductorcharge transfer device that precludes its practical use as a lightemitting device. Silicon is the preferred semiconductor material forconstructing such a device, and yet silicon does not have a directenergy band gap; hence it has a very low quantum efficiency andtherefore its efficiency as an electro-optical light emitter is poor.The available light emitted from such a device via recombination ofcarriers is generally insufficient for many imaging applications.

SUMMARY OF THE INVENTION

In conceiving an image source constructed according to our invention, wefirst appreciated that semiconductor-based charge transfer orcharge-coupled devices (hereinafter, such devices are meant to beequivalent) have proven to be advantageous in the fields of imagesensing and image capture. In our departure from the teachings of theprior art, however, we accordingly sought to achieve the benefits ofcharge-coupled devices in a novel image source. A brief introduction tocharge-coupled theory should first be understood.

A modern charge-coupled device typically includes ametal-insulator-semiconductor structure which stores and transfers datain the form of electrical charge. This structure provides a shiftregister configuration via two or more sets of conductive electrodesformed on the insulator-semiconductor structure. A DC bias is appliedbetween the electrodes and the semiconductor; clocking pulses areapplied to the electrodes that effectively invert the semiconductorsurface such that the minority carriers are drawn to thesemiconductor-insulator interface and collect in "potential wells" underthe metal electrodes. When the clocking pulses are sufficiently large,the minority carriers transfer from the area under one electrode to thearea under the next electrode and thereby follow the potential wellsproduced by the clocking pulses.

Hence, one very attractive feature for our contemplated image source isthat a full line segment of an image data signal (organized as a seriesof either analog, sampled, or quantized charge packets) could be rapidlystepped through a charge transfer structure. This feature is a distinctadvantage over known signal matrixing schemes, which must deliver theimage signal in the form of selected voltages on a conductive matrix.The contemplated charge transfer structure therefore does not sufferfrom the signal propagation delay, distortion, and signal loss found inconventional image source devices. A semiconductor charge-coupled devicestructure was also attractive due to its relative simplicity, low cost,and ease of fabrication.

Accordingly, we devised an image source which offers the benefits of asmall scale cathodoluminescent structure with a semiconductorcharge-coupled device structure. In doing so, we have discovered amethod and apparatus for converting time-varying serial electronic data(in the form of analog, digital, sampled analog, digitized sampledanalog, or other electronic signals) into discrete, high-resolutionpoints of light output. An image source constructed according to thepresent invention provides a high-resolution light image in response toserial electrical signal inputs. The contemplated image source isexpected to be relatively inexpensive to manufacture, simple to operate,and offers high reliability.

The contemplated image source operates from either continuous ordiscrete time domain image information. With a minimum of signalprocessing and driving logic the contemplated image source converts animage information electrical signal to discrete parallel light outputpixels. The output pixel level may be continuous or discrete, and thelevel may be modulated. The device offers close to true primary coloroutputs; a parallel 3-color capability is achieved by arranging threeparallel linear arrays. Image resolution above 1000 dpi may be achievedwithout the recourse to the complex and troublesome addressing,switching, or multiplexing schemes in the prior art.

The device is very efficient in converting the input signal to a lightoutput signal, and neither a high drive current nor high current drivecircuitry is required. Consequently, heat dissipation andelectromagnetic interference problems are obviated.

The contemplated device can be used in a digital saturation mode forhigher light output. By use of an electron current amplification(electron multiplier), a high intensity light output level may beachieved. Because an extremely fast write time is available, thecontemplated device may be successfully used in high-speed imageexposure or recording scheme .

The image source may be advantageously used in color image transmissionor reproduction apparatus such as facsimile machines;electrostatographic reproduction apparatus such as copiers, printers,and duplicators; photographic printing and reproduction apparatus; andflat panel displays for static and dynamic image information.

The contemplated image source includes a semiconductor charge-coupleddevice combined with a gated field emission array (the combination ofwhich is termed herein a CCD emitter), an electron multiplier, and aphosphor screen backed by a transparent conductive layer. The foregoingcomponents are supported and contained in an evacuated transparentenvelope. The CCD emitter, which accepts the serial image signal,converts the signal to parallel discrete electron emissions, themagnitude of which are proportional to the time amplitude of the imageinformation.

The emitted electrons are accelerated by an electrostatic field in theelectron multiplier. The electron multiplier also increases the currentdensity of each discrete emission so that an electron stream havingsufficient energy for the desired level of light emission will impactthe phosphor layer. The light emission may be viewed directly, to thusprovide an image display, or may be coupled to a photosensitive mediumby an optical coupler to thereby provide an image recording apparatus.

In one embodiment of the invention, the light output may be directedonto a photosensitive image recording medium to provide means for imagerecording. Of course, the light output from the contemplated imagesource is generally suitable for exposing any photosensitive medium soas to record one or more desired images.

Alternatively, we have devised second and third embodiments of thecontemplated image source, wherein the light output will form an imageto be viewed directly. Either of these contemplated embodiments maytherefore serve as an image display device. Further, the output of anyof the contemplated embodiments may further be collected and transmittedby light transmission means known in the art for remote image recording,display, or other types of processing.

The invention, and its objects and advantages, will become more apparentin the detailed description of the preferred embodiments presentedbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

In the detailed description of the preferred embodiments of theinvention presented below, reference is made to the accompanyingdrawings.

FIG. 1 is a simplified diagrammatic view of an electrostaticreproduction apparatus which incorporates an image source constructedaccording to the present invention.

FIG. 2 is a side diagrammatic view of the preferred embodiment of thecontemplated imaging source of FIG. 1 in its simplified form.

FIG. 3 is a side sectional view of a practical embodiment of the imagingsource of FIG. 2.

FIG. 4 is a simplified schematic view of the charge-coupled device (CCD)emitter section of the image source of FIG. 3.

FIG. 5 is a plan view of one portion of the CCD emitter section of FIG.3, with further sectional views in FIGS. 5A and 5B.

FIG. 6 is a schematic representation of a calibration circuit forcalibrating the contemplated imaging source of FIG. 3.

FIG. 7 is a side sectional view of a second preferred embodiment of animage source constructed according to the present invention.

FIGS. 8 and 8A are side sectional and front sectional views,respectively, of a third embodiment of an image source constructedaccording to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIG. 1, it will be appreciated that the invention tobe described herein will have great utility in an electrostaticrecording apparatus. However, an image source constructed according toour invention need not be limited to only one such application, as otherimage recording apparatus will benefit from this invention.

Accordingly, one preferred embodiment of an image recording apparatus 20includes an optical write head 21 which incorporates the contemplatedimage source. The write head 21 is fixed in spaced relationship with aphotosensitive material 22 disposed on a rotable drum 23 such that animage frame of the material may be exposed by relative movement therebetween.

The contemplated photosensitive material 22 is preferably aphotoconductive medium formed as an outer layer on the circumference ofthe photoconductive drum 23 which, in turn, is rotatably connected to adrive device (not shown) for rotation in the direction of arrow 24. Thewrite head 21 may alternatively be made movable for providing therequisite relative movement. The image source includes at its face a rowof light emission elements which will emit light in corresponding quantaknown as picture elements, or pixels, to form an electrostatic latentimage on the photosensitive material 22.

Around the circumference of the photoconductive drum 23, there aredisposed: a cleaner 26 for first cleaning the surface of thephotosensitive material 22, a charging corotron 27 for providing anelectrostatic charge on the photosensitive material 22, and the opticalwrite head 21 for forming the electrostatic latent image. A developmentunit 28 applies toner to the formed electrostatic latent dot image and atransfer corotron 29 is useable for transferring the toner-developedimage onto recording paper 31.

The requisite image data storage, processing, and delivery means(hereinafter data source 30) is interconnected with the write head 21 bya series of data links and control links shown collectively as line 30A.Data source 30 may include, depending upon the application, means toproduce print jobs as character code signals queued in a print server,and spooled one page at a time to a raster image processor (RIP). TheRIP converts the character code signals to a rasterized video datastream for printing line by line as will be described shortly.

The data source 30 may further include means for data compression, linestorage, data expansion, data resequencing, and page buffering (thelatter for storing image data as it is processed). A microcontroller maybe included to function as the system manager, overseeing the overalloperation of the apparatus 20. The microcontroller may handle data andcontrol communications and store the internal pointers identifying thebeginning and ending addresses for each image frame and for therasterized lines of image data that constitute an image frame. Themicrocontroller may also initiate transfers from the RIP and control thedata compression and expansion process. The data source 30 may alsoinclude a writer interface which prepares a full line of image data. Theforegoing components within the data source 30 are known in the art andthus are not discussed further.

Those skilled in the art will naturally find that modifications to theforegoing reproduction apparatus 20 will easily result in other types ofimage recording apparatus for exposure of other photosensitive media,such as photographic film. Such modifications and applications are knownin the electrostatographic, reprographic, printing, and facsimile arts.

The construction of the image source according to the present inventionis shown in FIGS. 2 and 3. FIG. 2 is a simplified diagrammaticrepresentation in a longitudinal sectional view of the contemplatedimage source, and FIG. 3 is a fragmentary side view of a first preferredembodiment of an image source constructed according to the presentinvention. It will be understood that the contemplated image sourcereceives data and control information from a data source as alreadydescribed with respect to FIG. 1.

A preferred embodiment 40 of the image source includes a combinedcharge-coupled device and integral field emission microtip structure(termed hereinafter the CCD emitter 42), an electron multiplier 44, anda phosphor screen adjacent 46 a transparent conductive layer 48. Theforegoing components are fixed in an evacuated, airtight transparentenclosure 50.

The CCD emitter 42 will be described in detail with respect to FIGS. 3,4 and 5. Although only one CCD emitter is illustrated, it iscontemplated that in practice a line of such devices will mountedlengthwise within an envelope 50 of suitable dimensions, whereby theends of adjacent CCD emitters are butted or overlapped to form acomposite interconnected linear set of the desired length. Image signalsintroduced to the first CCD emitter are accordingly stepped through itand through the length of the next adjacent device, and so on, until thefull complement of data is loaded. For clarity, however, only a singleCCD emitter will be described.

The CCD emitter 42 accepts serial, electronically-encoded time-domainimage data and converts the image data to parallel discrete electronemissions. In operation, the emitted electrons 52 are accelerated by anapplied electrostatic field E1 and thus are attracted to enter theelectron multiplier 44. The electrostatic field potential imposed acrossthe electron multiplier (E2-E1) increases the current density of theprimary electron emission 52. A further electrostatic potentialdifference (E3-E2) between the electron multiplier 44 and the conductivelayer 48 behind the phosphor coating 46 causes the secondary electrons54 to impact with sufficient energy upon the phosphor coating 46.Activation of the phosphor material is then achieved according to thelocation and intensity of impacting secondary electrons, the pattern ofwhich define a desired image segment. This pattern of light emission (apattern of picture elements, or pixels) is optically coupled to thephotosensitive material 22 by a suitable optical coupler, preferably inthe form of a gradient-index rod lens array 60.

Relative motion between the photosensitive material 22 and the imagesource 40, in a direction essentially perpendicular to the long axis ofthe image source, will allow subsequent rows of image data to be gatedinto the image source and converted to stripwise portions of an overallimage. Repetitive conversion of the serialized image data tocorresponding stripwise light emissions, along with relative motionbetween the image source device and the photosensitive material 22,allows a full frame of image data to be recorded.

It will be appreciated that with use of known image data formatting andtransmission means, such as a rasterizing image processor (RIP) (notshown), sequential rows of serial image data in the form of electricalimpulses is gated into the CCD emitter 42. Each row of data istransferred so as to fill the length of the CCD emitter, as will bediscussed with respect to FIG. 4, such that the cells of the CCD emitterare filled with discrete charges corresponding to the data to beconverted to light. Upon enabling the output of all the cells of the CCDemitter, the data can be nearly instantaneously converted to arespective stripwise emission of primary electrons 52.

In a purely indicative and in no way limiting manner, the components ofthe image source 40 will be described briefly, with a more detaileddescription to follow. In practice, a vacuum is maintained in theenvelope 50, and therefore signal, power, and ground connections to theCCD emitter 42, electron multiplier 44, and conductive coating 48 areestablished by use of axial conductors 62 which exit the envelope 50.The transparent envelope 50 is preferably made from glass.

Conductive coating 48 may be made from aluminum or gold, and insulatingportions 64 are made from silica.

In the embodiment illustrated in FIG. 3, the conductive coating islocated between the transparent envelope 50 and the phosphor coating 46,the latter then directly facing the electron multiplier 44. Theconductive coating 48 is preferably made transparent to the lightemission of the phosphor so as not to obscure the excited phosphoremission of light made visible through the transparent wall of theenvelope 50. For this purpose, coating 48 may be a tin-doped indiumoxide coating.

The conductive coating 48 may be eliminated if the phosphor coating 46is deposited on a portion of the interior surface 66 of the transparentenvelope 50, if the portion is formed of a material that is alsoelectrically conductive and connectable to a conductor 62.

The phosphor coating 48 is disposed on the underside of the transparentenvelope 50, such that light emission from the phosphor coating mayescape from the side opposite to its excitation. Suitable coatings areformed from crystals known in the art to emit light when energy istransferred to them upon electron collision. Cadmium, zinc, or acombination of cadmium and zinc form the basic building blocks of thepreferred crystalline structure. The phosphor coating 46 may also becomposed of zinc sulphide or cadmium sulphide.

Further details on electron stimulation of a luminescent coating, andoptimization of same, maybe found in "Selecting Phosphors for Displays,"Compton, K., Information Display, 1/89, pages 20-25; and "OpticalCharacteristics of Cathode Ray Tube Screens," EIA Tube EngineeringAdvisory Council (TEPAC) Publication #116.

The optical coupler 60 is preferably composed of plural gradient-indexcylindrical lenses 60A each having a parabolic refractive indexdistribution. When the parabolic refractive indices of the individuallenses 60A are aligned, the individual pixels of light emission from thephosphor coating are merged into a continuous image. Such lenses 60A areformed and precisely aligned between fiberglass-reinforced plastic walls(not shown) such that the coupler 60 may be precisely located withrespect to the luminescent coating. A suitable coupler in the form of agradient index lens array is commercially available as the SELFOC LensArray (SLA) from NSG American, Inc., a subsidiary of NIPPON SHEET GLASSCO., LTD., Tokyo, Japan.

Preferably the electron multiplier 44 is a channel electron multiplier(CEM) formed from a microchannel plate (MCP) having a large number ofchannels, each of which functions as an electron multiplier. When aprimary electron 52 enters the low potential end of a channel, andstrikes the sides of the channel wall, it produces secondary electrons54 which are accelerated along the channel by the electric field tostrike the wall again, thereby producing more secondary electrons 54.This process is repeated many times until a large number of secondaryelectrons 54 emerge from the other end of the channel.

One suitable microchannel plate electron multiplier is the High OutputTechnology Microchannel Plate (HOT MCP) offered by Galileo Corp,Sturbridge, Mass. Another suitable channel electron multiplier is knownas the multiple dynode layer microchannel plate, and offers high gainsat a low recovery time. The construction of this device is disclosed in"Multiple Dynode Layer Microchannel Plate", Bruce E. Woodgate, NASA TechBriefs, July, 1990. The named multiple dynode layer MCP incorporates astack of discrete microchannel plate layers that are constructed toprovide fast recharging of their microchannel dynodes. Each layerconsists of an insulating plate perforated with a completetwo-dimensional array of microchannels and a conductive plate thatcontains a matching set of microchannels. The microchannels in the twoplates are aligned; those in the insulating plate taper from a largerdiameter on the anode side to a smaller diameter on the cathode side.

Further details on the construction of a suitable electron multipliercan be found in the following references, the disclosures of which areincluded herein by reference: U.S. Pat. No. 4,482,836, "ElectronMultipliers", Derek Washington et al, Nov. 13, 1984; U.S. Pat. No.4,805,827, "Multiplier Element of Aperture Plate Type", Gilbert Eschard,Feb. 21, 1989; U.S. Pat. No. 4,825,118, "Electron Multiplier Device",Hiroyuki Kyushima, Apr. 25, 1989. Still further information may be foundin "Development Status of Microchannel Plate Photomultipliers", S.Dhawan, R. Majka, IEEE Transactions on Nuclear Science, Vol NS-24, No.1, Feb. 1977; "Channel Electron Multipliers", Edward A. Kurz, AmericanLaboratory, March 1979; and "Microchannel Plate Detectors", JosephLadislas Wiza, in Nuclear Instruments and Methods, 162 (1979), pp.587-601.

As shown in FIGS. 4 and 5, the CCD emitter 42 preferably comprises afour-phase buried channel linear charge-coupled device, although othercharge-coupled structures may be used. Control and input lines includephase lines PHL1, PHL2, PHL3, and PHL4, connected respectively to phasecells PH1, PH2, PH3, and PH4. Storage control line STL connects to astorage control cell STC, and a source (image data signal input) line SLconnects to a signal gate cell SGC adjacent an input signal diode ID.Transfer control lines TGL1 and TGL2 connect to first and secondtransfer gates TGC1 and TGC2. A control gate line CGL connects to acontrol gate cell CGC, which underlies the linearly spaced arrangementof plural microtip field emission arrays, or field emission cells FEC.Drain line DL connects with the drain cell DC to allow a resetting ofthe field emission cells FEC.

A charge level linearly related to the input signal on the source lineSL may be introduced to the signal gate cell SGC by any of severalmethods known in the art. For example, the image signal may be combinedwith an appropriate direct current (d.c.) bias voltage on the signalline SL. The potential well under the storage gate cell STC is filledwith a charge packet (hereinafter simply "charge") by biasing thestorage gate line STL positive and the input diode line IDL to a lowpositive value. After a discrete time domain signal appears on thesignal gate line SL, the input diode line IDL is again biased highlypositive to transfer some of the charge back from the storage gate cellSTC. Thereafter, the charge left under the storage gate cell STC will bea linear function of the signal level at the time of the transfer.

From the storage gate cell STC, the charge is stepped along the phasesPH1, PH2, PH3, and PH4 of the linear CCD 42A by the polarityrelationships of the bias potential applied each of the four phases. Inthis manner, the charge level corresponding to each discrete data signalelement on the serial input signal line SL will be stepped along thelength of the CCD such that each phase 2 cell PH2 eventually contains acharge representative of a respective portion of the image signal.

The timing of charge transfer is preferably synchronized with thefrequency of the input signal on the signal line SL. A row indicatorembedded in the signal element series can be used to trigger transfer ofcharge in the emission region and start the introduction of a new row ofdata elements into the CCD emitter.

For a continuous, rather than discrete, input signal, the signal gatewould be enabled for a short period after the fill period of the storagegate well. In this case, the charge transfer rate would be independentof the input signal rate; resynchronization of the charge transfer wouldstart with each new row of image data that is introduced.

In the preferred method for transferring charges from the phase 2 cellPH2 to the respective field emitter cell FEC for electron emission, thetransfer line TGC2 is activated first with a positive applied potentialwhile the drain cell DC is held at an appropriate high positivepotential. The N⁺ regions that underlie the field emission cell FEC arethereby set to the same potential.

All charges in the phase 2 cells PH2 are simultaneously gated to theiradjacent emitter regions FEC by operation of the first transfer gateline TGL1. The first transfer gate TGCl transfers the charges from thephase 2 cell PH2 to the N⁺ doped layer 72A which underlies the emittertip cell FEC. With the potentials of phase cells PH1 and PH3 held low, apositive potential on the second transfer gate line TGL2 allows thecharges to be transferred.

After the signal charge is transferred into the FEC, emission isrestrained by the absence of an activation potential on the control gateCGC. After raising the control gate line CGL to a high potential, allthe charges that had been transferred to each FEC are emitted tocompletion. Thus, the total charge emitted from each FEC is a functionof the charge transferred to that location by the CCD. After emission,the control gate line CGL returns to a low state and the CCD emitter 42prepares for the next emission.

Upon completion of emission, the N⁺ regions which underlie the emittercells FEC are reset to a high positive potential by the potentialimpressed on the second transfer gate TG2 and the positive potential atthe drain cell. The second transfer gate line TGL2 is therefore raisedto reset the N⁺ doped layer under the emitter tip cell FEC so that thenext charge packet can be received. It should be noted, however, thatthe act of electron emission may be sufficient in itself to cause the N⁺doped layer to reset, such that the second transfer gate cell TGC2 maybe omitted in some applications.

With the charge having been transferred from the phase 2 cells PH2,those regions become clear and ready to accept new signal charges.Introduction of a new line of signal charges is then initiated such thatafter a short time delay (approximately the time it takes to couple thecharges from the first element of the CCD line to the last element), allof the phase 2 cells PH2 contain charge again. The aforementionedemission gating sequence is again performed to provide another stripwiseelectron emission.

Other charge gating schemes that are known in the art may be used. Phasetwo cell positions PH2 are preferred as the parallel outputs of the CCDstructure 42A, but the CCD emitter structure may be modified for outputfrom any one of the four phase cells, as is known in the art.Alternatively, the illustrated CCD structure 42A can be modified asknown in the art to incorporate a two- or three-phase CCD structure.However, the four-phase CCD structure in the illustrated embodiment ispreferred as four phase construction is simpler to construct. A buriedchannel (BCCD) structure is preferred as it requires no bias charge(also known as a "fat" zero) for high charge transfer efficiency,exhibits little or no noise caused by the trapping of charge by fastinterface states, and offers a higher frequency response than asurface-channel device (SCCD) of comparable dimensions.

Further details on the fabrication and operation of the preferred BCCDand SCCD device structure contemplated for use in the present inventionmay be found in the following references: "Charge Coupled SemiconductorDevices", W. S. Boyle and G. E. Smith, Bell Syst. Tech. J., Vol 49, pp.587-593, April 1970; "The ABCs of CCDs", Electron. Des., Vol 23, pp.58-53, Apr. 12, 1975; Charge Transfer Devices, Carlo H. Se'quin &Michael F. Tompsett, Academic Press 1975; Microelectronic Devices,Edward S. Yang, MaGraw-Hill, 1988; "Charge Coupled Devices--AnOverview", Walter F. Kosonocky, 1974 Western Electron. Show and Conv.Tech. Papers, Vol. 18, Sep. 10-13, 1974, pp. 2/1-2/20.

FIG. 5 illustrates the electron emission structure in the CCD emitter ingreater detail. A silicon substrate 72 supports a plurality of fieldemitters 74 so as to comprise a field emission cell FEC. Each emitter 74is formed as a conic projection 74 from an electrically conductive N⁺region 72A in the silicon substrate 72. An N⁻ doped region 72C underliesa silicon dioxide insulating layer 72D which supports the phase 2channel PH2 and the first transfer gate channel TGC1. The control gatecell is CGC is thus operated as a control or grid electrode. This layeris uniformly insulated and separated from the substrate 72 by adielectric filler layer 77.

When a grid voltage V_(g) is applied, an intense field is applied at theemitter tip to extract electrons from the conducting tips 74 into thevacuum region between the CCD emitter 42 and the electron multiplier 42.Field emission is based on the quantum mechanical tunneling of electronsthrough the emitter/vacuum interface under the influence of the highelectric field, as is known in the art.

Although in FIG. 5 only a few emitters 74 are illustrated, it should berecognized that it is preferable and within the contemplation of theinvention to incorporate a large number of emitters in a field emissioncell FEC. As disclosed in U.S. Pat. No. 4,874,981, such a cell isgenerally referred to as an electron-emitting cold cathode array, and isalso known as a field emission array (FEA).

While from the broad standpoint the emitting tips 74 could be madeseparate from the silicon substrate 72, it is preferred for simplicityto integrate the N⁺ doped region 72A and the tip 74 in one structure.Moreover, the substrate 72 provides both the necessary electricalconduction for the tips and the structural support for the same. It isrecognized, though, that this structure could be fabricated differently;for example, the substrate 72 could include a thin film or the like onanother type of support. And, although the N⁺ doped semiconductor region72A preferably has a level of doping that provides a resistivity of theorder of 0.01 ohm-cm, higher resistivities may be used in certaincircumstances to further enhance the beam shaping effect of the field.

Emitter tips 74 may be made from lanthanum hexaboride or from one of themetals taken from the group including niobium, hafnium, zirconium andmolybdenum, or a carbide or nitride of said metals. The emitter tips arepreferably in the form of cones whose base diameter may be approximately1-2 μm and whose height may be approximately 1-2 μm. The thickness ofeach dielectric insulating layer 77 may be approximately 1-2 μm.Dielectric layer 77 may be composed of insulative material such assilicon dioxide or aluminum oxide deposited on the substrate 72 as athin layer.

The control gate CGC is made up of an electrode 76L and plurality ofannular openings 76R, each of which circumscribes an associated one ofthe emission tips 74. Linear electrode sections 76L extend betweenadjacent annular openings 76R and provide electrical conduction therebetween. The thickness of the control gate may be approximately 0.4 to1.0 μm and the holes therein (for passage of electrons) have a diameterof approximately 1.5 μm on 2 μm centers. The control gate electrode 76Lmay include a thin metal film of molybdenum or chromium deposited on thedielectric layer 77.

Packing densities as high as ten million emitters tips per squarecentimeter are known to have been fabricated. Miniaturization greatlyreduces the operating voltages necessary for field emission to takeplace. Both the insulating dielectric layer 77 and the electrode film76L are typically etched to provide a region for creating the emissiontip 74. That is, in order to achieve the desired field pattern in thestructure being described, it is desirable that only the electrodesections 76L be provided in the regions between adjacent emission sitesto provide paths to conduct electrical energy between the openings 76R.The layer of insulating material 77 is removed by etching along with themetal film 76 between adjacent emission sites to reduce its surface areato inhibit buildup of surface charge which may interfere withestablishing and maintaining the desired potential field pattern.

Because of the very small size of the emitter tips 74 and the proximityof the respective control gate annular openings 76R, the voltage neededto produce field emission ranges from only a few volts to about 100volts. The magnitude of the electron current will be a function of boththe charge in the N⁺ layer of the emitter and the grid potential.Typically, the grid voltage V_(g) range is from 50 to 150 volts with atip diameter of 300 angstroms. Field emission arrays are known tooperate below 100 volts anode potential and can have emission currentsper cathode of over 10 mA. In fact, for special applications, currentsof over 100 mA at about 200 V have been measured.

The emitted electrons emerge from the annular openings 76R withcorrespondingly low energies. Nonetheless, the present inventioncontemplates the use of multiple emitters in parallel to produce greatlyincreased emissions for a given applied acceleration voltage, and allowsany performance variations in the emitters in one emission cell FEC tobe averaged. Further, because of their capability for low-voltageoperation, the tips suffer less sputtering caused by ion bombardment.Tests have shown that at 20 mA per cathode, over 40,000 hours ofoperation is possible. Further details on the construction of a fieldemission structure suitable for use in the present invention may befound in the following references, the disclosures of which areincorporated herein by reference: U.S. Pat. Nos. 3,789,471, 3,812,559and U.S. Pat. No. 3,453,478, "Electron Emitting Structure" filed in thename of Kenneth R. Shoulders and Louis N. Heynick; U.S. Pat. No.4,857,799, "Matrix-Addressed Flat Panel Display", issued in the name ofCharles A. Spindt and Christopher E. Holland. Further information may befound in Vacuum Microelectronics 1989: Second International Conferenceon Vacuum Microelectronics, Turner (ed.), 1989; "VacuumMicroelectronics", SRI International Business Intelligence Program,Report No. 780, 1989, pps. 23-29; "Vacuum Semi R&D Picks Up", ElectronicEngineering Times, Jan. 29, 1990, pp. 35-38.

The predictability of emission using any selected voltage, andreproducibility of results, depends upon the ability to produce andreproduce like emitter tips 74 which are uniformly spaced with uniformapical angles. Such construction methods are known to the art and aredisclosed, for example, by methods described in U.S. Pat. No. 3,789,471or the Shoulders and Heynick U.S. Pat. No. 3,453,478, the disclosure ofwhich is incorporated herein by reference. Emitter tips that haveessentially identical configurations may be provided by means describedby C. A. Spindt in "A Thin-Film Field Emission Cathode" in the Journalof Applied Physics, Vol. 39, No. 7, pp. 3504-3505, June 1968.

As shown in FIG. 6, it may be necessary to calibrate the output of theimage source 40 on a pixel by pixel basis using a test signal from asignal generator 80. Light output of each pixel 81-1, 81-2, 81-3, . . .81-N along the length of the image source 40 is first measured by acalibrated photosensitive sensor 82. The measurement data is output to acomparator 84 for pixel-by-pixel comparison with a reference levelprovided by a calibrated level source 86. A timing signal from timingsignal source 80 is also input to the comparator 84. A response curve isgenerated by the comparator, which is stored in a pixel correctionnetwork 88 that precedes the image source 40 in the image data signalchain. Input signals to the image source 40 are thereafterpre-emphasized by the pixel correction network 88 to adjust the incomingserial image data signal.

As shown in FIG. 7, a second preferred embodiment 90 of the contemplatedimage source may constructed to provide an image display means. Aplurality of CCD emitters 92-1, 92-2, . . . 92-N (each being equivalentto the CCD emitter 42 of FIG. 4) are arranged in parallel rows on aplanar support 91. Each CCD emitter 92-1, 92-2, . . . 92-N is situatedclosely adjacent, if not contiguous with, the adjacent CCD emitters; thedevices are separated for clarity in the illustration. A single electronmultiplier 93 may be mounted against the output faces of the plural CCDemitters. The foregoing components are enclosed in an evacuatedtransparent envelope 95 having roughly plane parallel front and rearfaces 95F and 95R. A conductive coating 94 and a luminescent phosphorlayer 96 are incorporated in the front face 95F, which then serves asthe display face. Electrical connections (not shown) are providedthrough the envelope 95 to the components mounted within by conductormeans (not shown) similar to those previously discussed with respect toFIG. 3, or by means known in the art.

Each CCD emitter 92-1, 92-2, . . . 92-N is provided with one respectiveline of rasterized image data signal from an image frame; the totalcomplement of the CCD emitters thus can receive image data on aframe-by-frame basis. That is, any one image frame to be displayed isapportioned into sequential lines of image data that are respectivelydirected to successive (top to bottom, or vice-versa) CCD emitters 92-1,92-2, . . . 92-N. Such data may, for example, be provided by image framestorage and processing circuitry (not shown), which may include a rasterimage processor (RIP), as known in the art.

The processed image signals are provided such that the charge levelsheld therein (as was described with respect to FIGS. 4 and 5) are eithersequentially (row-by-row) or simultaneously (in flash mode) converted tomultiple stripwise electron emissions, which are then made more intenseby the electron multiplier 93. Secondary electrons from the electronmultiplier are attracted to the conductive coating 94 with sufficientintensity that the phosphor layer is activated in a respective imagewisepattern.

By activating the full complement of CCD emitters either sequentially orsimultaneously, a full frame of image data may thereby be converted to alight image which is displayed from the front face 95F. Due to thepersistence of light emission by certain phosphors, which may beselected as known in the art, the light image on the display face 96remains for a brief period such that a an image is recreated for viewingby a human observer 100.

If the conversion of the image signals is performed one line at a time,certain ones of the CCD emitters may be loaded with data while othersare in the process of providing an electron emission. Alternatively, anentire frame of image data may be entered into the full complement ofCCD emitters, after which the CCD emitters provide primary stripwiseelectron emissions sequentially or simultaneously. With a suitablerefresh rate, it is contemplated that the illustrated embodiment willprovide full-frame, high resolution display of image data. Theconversion of signals to light is extremely rapid and therefore dynamicdata signals, such as video image data, may be reproduced with very highresolution and at a high frame rate.

As illustrated in FIGS. 8 and 8A, a third preferred embodiment 110 ofthe contemplated image source may be constructed to provide anotherimage display means. A CCD emitter 112 (equivalent to the CCD emitter 42of FIG. 4) is provided within a transparent evacuated envelope 114having roughly plane parallel front 114F and rear 114R walls, the firstof which includes a display face 114D. Within the envelope 114 andincorporated into the interior surface of the front wall 114F are atransparent conductive coating 116 and a luminescent phosphor coating118; mounted in opposition to the display face, on the interior surfaceof the rear wall 114R, are a plurality of selectably operable verticaldeflection electrodes 120. Another set of spaced, selectably operableparallel acceleration electrodes 122 are provided proximate to the CCDemitter 112 also respectively at the interior of the envelope 114.Electrical connections to the foregoing components are made as known inthe art, preferably through the envelope ends (the ends of the envelope114 are perpendicular to the front and rear walls, and are not shown forclarity.)

The CCD emitter 112 is provided with a full frame of rasterized imagedata signals on a line-by-line basis. Such data may, for example, beprovided by video image processing circuits as are known in the art.Each line of image data is converted to a respective stripwise primaryemission of electrons 130 emitted orthogonal to the CCD emitter face andalong a path 132 spaced roughly equidistant between the front and rearwalls 114F and 114R. The accelerating electrodes 122 are thensequentially activated to provide an accelerating electrostatic fieldpotential such that the entire strip of emitted electrons 130 achieve aselected momentum in a direction parallel to the front wall 114F.

As the accelerated electrons on path 132 enter the zone behind thephosphor coating 118, the vertical deflection electrodes 120 areselectively activated to steer the electrons into the phosphor coating118. Accordingly, the data corresponding to one line of the image frameis converted to a corresponding stripwise light emission. By rapidlyinputting in succession the data corresponding to the remaining lineportions of the image frame, and accordingly altering the characteristicand timing of the electron acceleration and vertical deflection, a fullframe of dynamic image data may be reproduced on the display face 114D.Subsequently, the entire image frame may be refreshed in a continuous,high-rate repetition of the foregoing steps. Changes in the image frameinformation content may be accommodated nearly instantly.

To accomplish a three-color display of respective color image data, thephosphor coating is preferably composed of plural sets of three-colorphosphor segments. The foregoing stripwise emission of electrons ismodified to a succession of three single color stripwise emissions, eachof which being driven by corresponding lines of single color image data.Each stripwise electron emission is directed by the deflectionelectrodes into a respective one of the three colored phosphor segments.With successive line emissions, repeated at a high rate, an entire threecolor image frame is activated for display at the phosphor coating.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

What is claimed is:
 1. An image display device for converting pluralelectrical charges representative of image information, the chargesbeing organized in line segments, to a respective imagewise pattern oflight for direct viewing, comprising:a plurality of CCD emitters, eachhaving a charge-coupled device for storage and transfer of the chargesin plural cells therein and plural field emission means integrallyaligned with predetermined ones of the charge-coupled device cells, eachfield emission means being adapted for providing field emissionscomposed of primary electron emissions derived from the charge in therespective charge-coupled device cell; electron multiplier means,aligned with the CCD field emission means and adapted for receiving theprimary electron emissions and for providing corresponding secondaryelectron emissions of selectable intensity having increased currentdensity relative to the primary electron emissions; and luminescentmeans, aligned with the electron multiplier means, for receiving thesecondary electron emissions and for outputting the imagewise pattern oflight, whereby the secondary electron emissions impact the luminescentmeans with sufficient energy for an improved level of light emission. 2.An image display device for converting plural electrical chargesrepresentative of image information, the charges being organized in linesegments, to a respective imagewise pattern of light for direct viewing,comprising:a CCD emitter having a charge-coupled device for storage andtransfer of the charges in plural cells therein and plural fieldemission means integrally aligned with selected ones of thecharge-coupled device cells, each field emission means being adapted forproviding electron emissions derived from the charge in the respectivecharge-coupled device cell; electron acceleration means, aligned withthe CCD emitter and adapted for accelerating the electron emissions;electron steering means for directing the accelerated electron emissionsin a selected beam path; and luminescent means, located in the beampath, for providing light output according to the electrons directedthereon.
 3. An image display device for converting a line of serialelectrical charges representative of image information into a respectiveimagewise pattern of light for direct viewing, the image display devicecomprising:a semiconductor charge-coupled device for transfer andstorage of the electrical charges in respective charge-coupled devicecells therein; a plurality of field emission cells, wherein each fieldemission cell is integrally aligned with a selected one of thecharge-coupled device cells, and each field emission cell includes aplurality of microtip emitters; charge transfer means for transferringselected charges from the charge-coupled device cells to the respectivefield emission cell; activation means for activating field emission ofthe transferred charges from the microtip emitters in selected ones ofthe field emission cells to provide field emissions composed of primaryelectron emissions; electron multiplier means, aligned with the pluralfield emission cells, for receiving the primary electron emissions andfor outputting corresponding secondary electron emissions of selectableintensity having increased current density relative to the primaryelectron emissions; and luminescent means, aligned with the electronmultiplier means, for receiving the secondary electron emissions and foroutputting the imagewise pattern of light, whereby the secondaryelectron emissions impact the luminescent means with sufficient energyfor an improved level of light emission.
 4. The image display device ofclaim 3, wherein the transfer means provides simultaneous transfer ofcharges from plural charge-coupled device cells to the respective fieldemission cells.
 5. The image display device of claim 3, wherein theactivation means provides simultaneous primary electron emissions fromplural field emission cells.
 6. The image display device of claim 3,wherein the charge-coupled device cells are formed from ametal-insulator-semiconductor structure.
 7. The image display device ofclaim 3, wherein the charge-coupled device cells include aburied-channel structure.
 8. The image display device of claim 3,wherein the charge-transfer means includes means for four-phase stepwisestorage and transfer of the charges therethrough.